Multifrequency generating and selecting system



July 20, 1948.

M. L. DOELZ MULTI-FRQUENCY GENERATING AND SELEGTING SYSTEM Filed Feb. 27) 1946 /VEL v//v l, Dot-Lz IN V EN TOR.

Patented July 20, 1948 MULTIFREQUENCY GENERATIN G AND SELECTING SYSTEM Melvin L. Doelz, Minneapolis, Minn., assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application February 27, 1946, Serial No. 650,666

` 15 claims. (ci. 25o-36) stability and their fundamental or base frequency tends to depart from desired fixed value. In other Words, the resultant harmonics` are greatly dependent upon temperature, humidity and similar ambient .conditions affecting not only the generator tubes but also the components which determine the fundamental or base frequency. The third general type, has the advantage of stable fundamental frequency. In Iall the prior known arrangements, it has been extremely difficult without the use of extremely complicated and expensive duplicate equipment, to produce selectively any one cf a large series, for example several thousand, of highly stabilized frequencies closely spaced in the frequency spectrum.

Accordingly, it is one of the principal objects of this invention to provide an improved system for selectively obtaining any one of a large series of frequencies closely spaced in the frequency spectrum, and with the same degree of frequency stability as is obtained with 'a stabilized generator such as a crystal-controlled oscillator.

Another object is to provide a system of producing any one of a series of frequencies over a. very wide range of frequencies, and with substantially the same degree of stability in each selected frequency as that of a crystal-controlled oscillator.

Another object relatesto a system for producing any one of a great number of carrier frequencies by using a master oscillator of the crystal-controlled type, and deriving under control thereof the desired frequency by multiplication and frequency conversion processes without correspondingly multiplying errors which tend to develop in the frequency conversion stages.v

A feature of the invention relates to a system for producing any one of a very large series of radio carriers by separating the output of the master oscillator into a plurality of frequency selector channels, and into a multiplier channel, and combining the outputs of all the channels so as to selectively obtain-the desired frequency with exactly the same degree of stability as that of the master oscillator.

Another feature relates to an improved instrument which will select and emit any one of several thousand equally spaced frequencies within a high frequency range, for example of 20 to 40 megacycles. ture,` each desired frequency is derived under control of a crystal-controlled master oscillator input operating for example at 100 kilocycles by combining exact multiples and sub-multiples of the master oscillator frequency through the intermediary of adjustable local conversion oscillators, in such a Way that any undesirable error in the local oscillator or local oscillators are automatically cancelled out. The desired frequency is selected from, rather than controlled by the multiples and sub-multiples of the master frequency, and are, therefore, independent of the Y small variations in values of the circuit components such as are normally encountered in the electronic circuits. As a result, the accuracy in percent of stability of the selected output frequencies is exactly that of the master oscillator.

A further feature relates to an improved instrument for selectively producing under control of a master oscillator, such as a piezo crystal-controlled oscillator, any one of a large series, e. g.. several thousand, of radio carri-ers which are Very closely spaced in the frequency spectrum, and by employing only two calibrated dials. These dials need not be calibrated to hair-line accuracy since the Iaccuracy of the selected output frequency is determined primarily by the accuracy of the master oscillator.

A still further feature relates to a system for deriving any one of a series of high frequency carriers under control of a master oscillator by subjecting waves derived under control of the master oscillator and in separate frequency selector channels to alternate addition and subtraction in respective frequency conversion stages in each channel so as to eliminate ambient errors in the local conversion oscillators in each ccn- Version channel; and by subjecting Waves derived from the master oscillator to a frequency multiplyingaction. The waves derived from the respective selector channels and from said multiplier channel are combined so as to produce any desired frequency among several thousand with the same order of stability as that of the master oscillator. This result is achieved through the In accordance with this feai selector channel vact'sto select" subdivision incre` ments within the said widely spaced increments. A still further feature relates to the novel organization, arrangement and relative intercon" nection of parts which cooperate toproduce an improved and highly stable multi-frequency generating and selecting system.

Other features and advantages'not specifically' enumerated will be apparent after a' consideration of the following detailed descriptions and the appended claims.

Referring to the drawing, there is shownl a master oscillator I, which is preferably of the grid-controlled vacuum-tube type H, whose frequencyis stabilized bythe piezo crystal l2 in the well-linow manner. Merely' for explanatory purposes, it ywill be assumed that oscillator I generates atv a fixed frequency of' 100 kilocycles. This n. oscillator controls three separate channels identified respetively'as' Selector -channel A; Selector channel B;V and` Multiple` generator ch'anrrel'f'A vThe selector channelji .is controlled byv e] frequency subdivider I3 of any well-known ki dgwhereby thereis produced a sustained frequ n cyrwave which is one-half the'frequency of oscillator I'Q; r`1a rx1ely,'5 'Y kilocycles'. .Lilewise,I the sel1`; c tcrr*channel* Biaisl controlled' by a frequency subdivideirlmld; whichV receivesuthe" 50 kilocycle waves `from vdivider [3, and further subdivides them rinto,sustained frequency waves-which are one fth'thefrreque'ncy of the waves from' divider l` andtherefore;one-tenth the frequency ofthe wavesV frornwoscillator lll, namely, l kilocycles. Eer ajdescriptionjof typical frequency subdivider arrangements that may be" used'for the devices lffand 14, referencemay be had to Electronic Engineering 4Handbook,` Batcher a'nd Moultic, page .3111., The master oscillator lil' also controls the'multple generator channel where it is subjected; to a first frequeney'multiplier' 1.5, whicn may yhave a 'multiplying' factor ofy 10 to produce an outputjat' 11,megacycle.` This output ispassed mrougntnei meeacylemter as, anu thence t'o' a second multiplier stage^ Il, which may have a multiplying factor of 5V to produce aY 5v megacycle output. 4 fffljlese latterv waves-are then passed through a 5' megacycle flterlgi, whose output i's further` multiplied l, in frequency by frequency multiplier IVS, which has a multiplying factor of signal. For a detailed description`- ofr suitable frequency multipliers that l may beuse'd for the devices I5,V ily and' i9, reference may be had to Radio Engineering, by F. E. Terrna'ri', pages 33e-.341, ,l

,t r he 50 ,kilocy'clgf waves from device I3`are applied' tor any harmonic Yproducir'ig device such a`s overdrivenj grid-controlled vacuum tube 2l, which produces in its output a spectrum of harmonicsfof the input frequency as described for 'niarnfpleIinl Radio Engineering, by F. E. Terman, ist' edition, pages 221-225, published'by McGrawljlillV B ook Company, Inc., New York, N. Y. If desired, the device 2i v4may be any well-known form of; wave distorter which is rich in harmonics ofua .fundamental input frequency, such' for ex'- amplev as'ahywell-lnown form of multi-vibrator circuit such as de's'zrib'ed inpagesI 275-276 f book by F. E. Terman. Associated with the output of device 2l is an adjustable band-pass ,4 filter 22, which is designed to pass a frequency band of 6.7 to 8.7 megacycles. Filter 22 is of a type which is capable of selectively passing with substantially uniform gain any desired narrow band-width of frequencies in its acceptance band ovf` 67 ti8s7 meg-acyclesf VIt'may takeany welllrn'ow'n form; such'for example-asa permeability tuned inductance with an adjustable permeability magnetic core. The pass-band at any given setting of filter 2 2 should preferably not exceed 700 kiicyclesorieithr side of the desired frequency settg'uflg.` 'Ifheuwaves passed by filter 22 are applied toany welll-known form of frequency mixer whichforf'example may be any of the known tzypesfoffr'equency converter tubes used in superheterodyne radiorv receivers and the like. Associated with filter 22 and mixer 23, is an adjustablel frequency oscillator 24, which is of the free running type as distinguished from a stabilized oscillatorl such a`sa crystal-controlled oscillator;A Oscillator' 2'4 isdesigned' to be adjustable' so? asto` generate 1 any fundamental frequency inf-thev band' to"`4 megacycles, andI its output circuit is such that it selectively passes withnia'ximum gain'the'se'cond harmonicof the generated fundamental frequency, namely, any frequency between 6 to 8 megacyclesr This second harmonic' is impressedk upon-the mixer 23, where it beats with thel 67- to: V8:7 megacycle signal from filter 22. The tuning ,elements 2E and 2'5`of lter 22and' oscillator 24,'a're respectively ganged together so asto-'p'roduce'forr all settings"in'conjunction withthe usual intermediatefrequeri'cy coupling circuits; a-'constant interme'diat'ecarrir frequency' e. g.; of 700 kilocycles whichis ampliedinth intermediate frequency ampliier 21.-v InTA other words, theoutput of amplifie'r 2T consists" only of the intermediate frequei'icy carrier' representing'the"difference frequency between' the frequency settings of `elenients V22' and1 24;v

The intermediate' frequency carrier wavesfrom amplifier 27 are then'impressed' onaV` mixer devicev 28 similar t'o device 2l: At the sameftime, niej se'nulharmoniefrom oscinator 24'- ispassed throughi a 6 to" 8 mega'cycle band-pass, filter' 29, the tuning element" 3l) ofL which is `ganged for unitary' operationt' the aforementioned tuning `frequenc'zy carrier waves from ampliher 21 and the'A 6" t'oi 8` me'gacycle waves from filter 29 are selected by the adjustablel filter 3|, which is similar tc'rlt'err 22, and-has an acceptance band 6.7 to 8.7 m'egacycle's;V Thev tuning element 32 of lter 3| is ganged'l to the' tuning elements 25, 26 and 30' for unitary operationtherewith.` As a result of this alternate subtraction' and addition in the mixers* 23g and 28; by the ymeans described, the stability of any selected frequency inthe band 6.7 to 8.7 megacycles in the output oflter 3|, is determined' primari-ly yby the' stability of Vthe master oscillator l0, and is entirely independent of; ambient changes inthe frequency of oscillator 24', such' for example as those resulting from humidity' variations; temperature variations and the like. By this' method; it, is possible -to select any frequency inthe range16.7 to 8.7 megacycles with asgreata' percent` ofv lstability as that of oscillator l0: The output of lter 3| is then multiipliedr in a frequency multiplier 33, which has a multiplying factor ofv 10 to produce any selected frequency in the' range 67 to 87-,megacyc1es- The selected frequency is then passed through an adjustableV band-pass filter 34 covering the 67 to 87 megacycle band, the tuning element 35 of which is ganged to the aforementioned tuning elements 25 and 26, 30 and 3l.

The adjusting knob 36 which 'controls the ganged tuning elements is provided with a calibrated scale, which may have, for example, 40 main subdivision markings each representing a .5 megacycle step and covering the range from 67 to 86.5 megacycles. By this arrangement, one of 40 groups of frequencies each of .5 megacycle width in the 67 to 36.5 megacycle band can be selectively chosen by setting the knob 36 to the particular one of its 40 separate settings.

The selector channel B is substantially the same as channel A as far as filter 3I,exceptthat channel B is arranged to Select in 50successive steps of kilocycle spacing or width, in the range 3.0 to 3.5 mega-cycles, by means of the unitary adjusting knob or dial 31.

With the examples of frequency given for channel A, the 10 kilocycle waves from subdivider I4, arepassed through the distorter 38 similar to device 2l, and the adjustable bandpass filter 39 which corresponds to filter 22 passes only frequencies in the band 3.0 to 3.5 megacycles. The local adjustable oscillator 40 similar to oscillator 24, is arranged to generate any fundamental frequency in the band 1.35 to 1.6 megacycles, and the second harmonic thereof is impressed upon mixer 4l, which corresponds to mixer 23. The waves from devices 39 and 4B, after passing through the mixer 3|, are converted into beat frequencies and the lower or difference frequency of 300 kilocycles is selectively amplified in the intermediate frequency amplifier 42 correspond ing to amplifier 21. The second harmonic from the oscillator 4l) isV also passed throughk the adjustable iilter 43 ycorresponding to filter 29, and

the output of amplifier 42 and the output of lter 43 are impressed upon the mixerl device 44 corresponding to device 28. By means of the adjustable band-pass filter 45, the "sum frequency in the output of mixer 44 is selected by the filter 45. 'The tuning elements 45, 41, 48 and 43 are ganged together for unitary operation by the'single knob 31, which cooperates with a calibrated scale which may be marked vin 50 subdivisions representing 10 kilocycle steps.

Assuming that the desired frequency is to vbe used as a transmitting carrier frequency, the switches 55 and 5l are in the positions shown in thedrawing. As a result, the 50 megacycle waves from the multiple generator channel are applied through switch 55 to the 50 megacycle lter 52, the output of which is applied to the mixer device 53, which may be similarto devices such as 23. Also impressed upon the mixer 53 is the selected frequency in the 3.0 to 3.49 range at the output of iilter 45. The mixer 53 is connected to a band-pass filter 54 which covers the range 46.5 to 47 megacycles representing the difference frequency between the output of filter 52 and the output of filter 45. The selected frequency in the output of Vfilter 54 is then applied to another mixer device 55, similar to devices such as 23, upon which the output of filter 34 is also impressed. By means of a suitable filter 55, the difference frequencies between the outputs of lters 34 and 54, are selected and passed to the terminal 51, whence they may be connected to any Well-known form of radio transmitter to act as the carrier or for any other purpose desired. The net result is that at the terminal 51, there can be produced in successive 10 kilocycle steps any one of 2000 desired frequencies in the range from 20 to 40 megacycles,l andeach of these frequencies has exactly the same frequency stability as oscillator l 0. In operating the device, the knob 35 is rst set to an appropriate position representing the group in which the desired output frequency is located. The knob 31 can then be adjusted to a point representing the particular frequency in the selected group. If the terminal 51 is to be used for radio reception purposes, the switches 50 and 5| are operated so as to replace the 50 megacycle filter 52 by a 55 megacycle lter 58, and also to replace the Vf6.5-4.7 megacycle filter 54 Vby a 51.552"megacycle lter 59. The

mixer 53 is also replaced by a similar mixer 60.

The elements 58, 59 and 60 function exactly the same as the corresponding elements 52 53 and 54, used for transmission, except that in this particular case the 2000 frequencies which result at the terminal 51 are in the band 15 to 35 megacycles which is a separate band from that above described for transmission, namely, 20 to 40 megacycles. While in the foregoing description, reference has been made to particular frequencies and ranges of frequencies, it will be understood that these are given merely for illustrative purposes, and for simplicity in explanation.

While certain specific embodiments have been disclosed herein, various changes and modifica# tions may be made therein without departing from the spirit and scope of the invention,

What is claimed is:

1. A selective multi-frequency producing system comprising a master oscillator, a plurality of frequency selector channels, a frequency multiplier channel, each of said selector channels being supplied with any selectable control frequency in a series of control frequencies derived from saidmaster oscillator; 'each selector chan'- nel including a localsource of adjustable frequency oscillations, means to combine the said series of control frequencies with a selectable frequency from the local oscillator to produce a series of beat frequencies, means to select a particular beat frequency, and means to combine with said particular beat frequency the frequency from the local oscillator to produce a resultant beat equal to theselected control frequency, and means to correlate the control frequencies applied to each channel so that there"appears in the output of one channel 'any one of a series of frequencies spaced apart a cycles per second in a predetermined range, and at the output of the other channel there appears any one of a series of frequencies spaced apart b cycles per second Where a and b are related by an in'- teger.

2. A frequency producing system according to claim 1 in which a separate frequency multiplier channel is controlled by said master oscillator, and means are provided for combining the output frequency of one of said selector channels with the output frequency of said multiplier channel tonproduce a desired frequency spacing between the output of the rst channel and the frequency of said combined output.

3. A selective multi-frequency producing system, comprising a Vcrystal-controlled master oscillator, a first frequency selector channel, a second frequency selector channel, means to de rive from said master oscillator a first series of control reQuenCies-meansto derive from said master oscillator a second series of control frequencies both series being electrically locked to the frequency of said master oscillator, filter casacca means-for'tlienrstfcnannel:navingfanlacceptancebandfwldtllcommensuratefwitir tliewidtn ofthe saldi first series;- andY adj ustable tot selectA there from aiI predetermincd frequency lik', other? filter meansV lfavingI ane-acceptance bandcommensurate Withltlie width ofi' saidsecondf ser-iesfandfadjust1- ab'le to" select therefrom a' predeterlminedv fre*-l quencyFr; a frequency'conversion system-in said first channel including a'- local' conversion oscillater# which? can`y loe-seti toi produce" any frequency: inaffband of thessamewidth as' the acceptance band of? the first-mentionedllter meansiloutlhav:V ing lai frequency diierenceFzvl/ithssaid frequency means-r tor mix? a frequency from trie local oscillatorvvitli said# frequencyiFs-,\ means ft'o selectk from" theresultant I'nixture'- theL frequency Fd; ctler means f to-VA mix: Witli said selected4 resultant Faf a frequency' Which is the; same:` as the` said frequency'from said local oscillator to?l obtainzza frequency" Fs Whose' frequency stability-A issub: stantiallyl independent of' ambient changes in said' local oscillator; a". frequency conversion: sysL4 tem nrsaid` second cnannelfincluding aloca'licon'- version*oscillatori'vvhichiis settable'=to produce'any frequencyfinlai band of the s'arnewidth"` as the acceptance band of the' second-mentioned? filter means buthavingaffrequencydifferencel Fd'fwith said frequency means; to' mix the' frequency from the" local oscillator" of the. second-channel vvritn said' frequency F5', means :to select' from: the resultant mixture the* frequen'cyb' Fa; other means to mix with said selected resultant a frequency whichy is'f'tliesame asthe" said? frequencyfro'm the local oscillator oft'he second channel toL obtain av frequency Whose -irequen'cy stabilltyis s'ubstantially independent of ambient changes in: said local oscillator of thesecond ch'anneiyand means to' combinelt-hef outputs-f of the'tWo channels-so that the settingv of one` channel produces freque'ncie's Within" a desired range with-L group spa'cings between successive frequencysettings a'n'd the setting' of the other channel produces frequencies which are' integral subdivisionsrofll the sety groupL frequencies of the? first channel;I

4"; A selective multi-frequency' producing system: according to' cla-im'l 3in1 which: the saidA filter means of eachichannelfr is g'angedltofthe frequency adjusting elementof thev local oscillator off the same channelto maintainsaidfrcquency Fe' constant' for al1-settings.

5. A selective multi-frequency' producingsys"- tem` according to claim- 3f inf Whichitiie'outputV of the frequency converter system in'.I each: channel hasan adjustable' filterV similar tothe saidf filter means: of the corresponding channel' andthavin'g its adjustingie'lement g'arged tl'ieeto".v

6. A multi-frequency selective system compris'- ing af masterY oscillator',l means including a first distorter for deriving under; control; of said master oscillator a erst series of frequencies, means'vincluding' a second distorter' for deriving"V under control of said master oscillatorl a secondi series of frequencies, an adjustable filter' for selecting from the fir-sti series'l a restricted band including a frequen'cyFa, a pluralstage frcqu'erfcyconverter system upon which saidlrst series is impressed, Said converter' producing" at its' output lhi salme frequency' as ilipressed'idn its input by" alternate additions* and? subtraction-s from a local conversion' oscillator; another adju'stalil'el filter for selecting'. froml the second series a restricted. band including a frequency" aplural stage? frequency convrsionsystem upon-Which the second series is impressed, s'ai'd convar'sin producing at its outputr thel sama frequency as? is: impressed los,

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on its .input by alternate f additions and; subtracr tions? fromv a1 locali conversion oscillator; afre-'f quenoy multiplier channel connected to said master oscillator; means to mix'the outputlof'the second-mentionedfrequencyy conversion: system Wit-hthe.' output of said' frequency' multiplier, means` to` select fromi said mixture a resultant! band'offrequencies; and means'to` mix the out-v put ofthe first-mentionedfrequency conversion system with: the f said resultant bandl to.A produce;v a. sericsfof frequencies each of which haslsubstantially the samefrequen'cy stability asthat'of said .master oscillator.

'7. In a frequency-selectingy system;y a crystaif co'n'trolledmaster oscillator, a pair of frequency selector channels; a frequency subdivider and harmonic-generator connected-between `saidfoscil-r lator and' each of said channels;' an' adjustable input filter connected tofthe'output of tlfeihard monic generator of tleflrst channel,- an' adjustable frequency conversion" oscillator for' the first channel; a: mixer device-connected to said filter and: oscillator toproduce an intermediate'fre quency'; `another'mixer device linsaid first channel uponl Which the said' intermediateY frequency is impresssed' and also' a conversion fre'quency'from saidoscillator, a second adjustable lilt'er connecte'dl tothe output of said second mixer, said first and second mixers producing equal but op; posite changes in the conversion' frequency from' said oscillator whereby thefoutputfrequency'from the'second mixer' is the same as the: frequency selected by the" first-mentionedlfilter, the acceptanceV bands of both said'lters'being substantially alike, and? the' adjusting' elements ofi said filters andjsaiolV local oscillator beinggangedv together" to produce in the first channel. output' group' frequencies; an' adjustable input ilter'connected' to the output of theharm'onic generatorof the's'e'oond channel, an' adjustable fre'quencyconverslon oscillatorfofr' the second' channel; afirst mixer device connected to said filter and oscillator' to produce an intermediate frequency, a` second mixer* deviceupon which the' last-mentioned intermediate frequency is impressed andf also a conversion frequency from the last-mentioned conversionA oscillator, another adjustable filter connected'to" theoutput' of the said mixer of said second channel, saidmixerdevices of the second channel producing equal butY oppositeAv changes in thel conversion frequency from the'l asssociated conversion oscillator' whereby the' output frequen'cy from the second mixer of the second channel is" the same as-the frequency selected' by the said input filter of the second channel,. the acceptance bands of bothI said filters' of the'fsec'- ond channel being substantially alike, andv the adjusting elements of. said filters andy said local oscillator of the second channel being ganged together toY produce at the output of the second channel equally spaced frequency increments representing integral' subdivisions" of the group output frequencies of the first channel.

8'. A frequency-producing and selecting system COmpTi'Sig a crystaleccntrolled master oscillator, means to' derive fro'rnsaid oscillator and in sepa rate channels tWo different series of. frequencies locked to the master oscillator frequency, fre'- quency conversion means in the first channel including an adjustable input filter having an acceptance. band commensurate withV the rst of said series', a local conversionv oscillator, a plu.- r'alitty of successive mixer stagesI connected to said-input filter" and said conversion' oscillatorY to produce at theA outputA of the last mixer stage a frequency which is thel same as the; input frequency selected by said input filter by alternate additions and subtractions with respect tothe conversion oscillator frequency, anoutput adjustable filter having substantially the same acceptance band as said input filter, means for gauging the adjustable elements ofthe saidl filters and theV said oscillator; frequency-conversion means in the said second channel having an adjustable input filter with an acceptance band commensurate with the said second series, said conversion means including a plurality of successive conversion stages with a common local conversionv o-scillator, whereby the output of the last stage has the same frequency as the selected input frequency from said input filter by alternate additions and subtractions with respect to the associated conversion oscillator frequency, an adjustable output filter connected to the last mixer and having substantially the same acceptance band as the input iilter of .the second channel, means for gauging theadjustable elements of both filters and of the associated local oscillator together; and a common combining network upon-'which the output of the rst channel andthe output of the second channel are impressed whereby the first channel can be set to produce a series of frequencies with uniform group spacings and the second channel can be set to produce a series of frequencies representing integral subdivisions of each of said groups of frequencies.

9. A system according to claim 8 in which the said means for deriving said two series of frequencies comprises two frequency dividers which are controlled by said master oscillator, the first frequency divider having connected between it and the said input filter a first channel a harmonic generator, and the second frequency subdivider having connected between it and the adjustable input lter of the second channel another harmonic generator, said frequency subdividers being connected in series with respect to the master oscillator.

l0. An instrument for producing any desired highly stabilized frequency within a relatively wide range of frequencies comprising a crystalcontrolled master oscillator, a first frequency conversion channel connected to said master oscillator through a frequency subdivider and harmonic generator, a second frequency conversion channel connected to said master oscillator through a second frequency subdivider in series with said rst subdivider; each of said frequency conversion channels comprising a pair of mixer devices, means to apply to the mixer devices of a given channel the same local conversion oscillation frequency, means to apply to the 'first mixer device of each pair a respective selected frequency from the output of the corresponding harmonic generator, and means to select from the output of the second mixer of each pair a respective frequency which is the same as the said respective selected frequency by alternate additions and subtractions in said mixers with respect to their local conversion oscillator frequency; a single adj usting means for selecting the output frequencies of the rst frequency conversion system in relatively widely spaced frequency spacings, another single adjusting means for selecting the output frequencies of the second frequency conversion system in relatively narrowly spaced frequencies representing integral subdivisions of said widely spaced frequencies, and a common combining network for the outputs of both said frequency conversion systems for selecting any 10S particular frequency which frequency has substantially the same stability as that of said master oscillator.

11. A system according to claim 10 in which said master oscillator is connected to a frequency multiplier channel, the output of which is mixed with the output of the said second frequency conversion system and said common combining network includes a mixer device upon which the output of the first-mentioned frequency conversion `system is impressed and upon which the mixed output of the second frequency conversion system and said frequency multiplier channel is impressed.

l2. A frequency-selecting system comprising a pair of channels each including in sequence a frequency subdivider, a harmonic generator, an adjustable input lter, a first mixer, an intermediate frequency amplier, a second mixer, and anV adjustable output filter; a local frequency conversion oscillator for each channel and connected to the rst mixer and also connected to the second mixer of the respective channel through a third adjustable filter, the adjusting elements of all said filters for each channel and for the adjusting elements of channel oscillator being ganged together; a common crystal-controlled master oscillator connected to said frequency subdividers, a frequency multiplier channel connected to said master oscillator, a mixing network upon which the output of said multiplier channel is impressed and upon which the output of the second of said pair of channels is impressed, and another mixer device upon which the output of the rst of said pair of channels is impressed and upon which the mixed output of the second of said pair of channels and said multiplier channel is impressed.

13. A system for selectively producing any one of a great number of high frequency carriers, comprising a frequency stabilized master oscillator, a first frequency selector channel for producing coarse frequency increments of the same frequency stability as said oscillator, a second frequency selector channel for producing ne frequency increments of the same frequency stability as said master oscillator, a third channel for producing a fixed frequency which is a multiple of the master oscillator frequency and having the same frequency stability, a coarse frequency subdivider connected between the master oscillator and said rlrst channel, a fine frequency subdivider connected between the master oscillator and the said second channel, the rst channel having at least two frequency conversion stages both of which are supplied with selectable local beating oscillations of the same frequency from a local free-running oscillator, the second channel also having at least two frequency conversion stages both of which are supplied with selectable local beating oscillations of the same frequency from a local free-running oscillator, and a frequency mixer electron tube arrangement connected to the said three channels and controlled by their output to produce by frequency conversion any desired high frequency which has the same frequency stability as said master oscillator.

14. A system according to claim 2() in which means are provided to select from the output of the rst frequency conversion stage of the first channel the difference frequency for application to the input of the second conversion stage of said first channel, means are provided for selecting from the output of the said second frequency conversion stage of the first channel the sum frewenn# channel; and the said second channel has means fouselecting froml the.output.fof; the `Afirst frequency: conversion. f stage. thereof.. the .difference frequencylfor application, to thenput .-of thesecond :frequency conversion. stage. of:A said second. channeh and` meansare 131:ovidec1..4 for selecting from theutput. of. the. second frequency conver-- sion stage .of,.said. second. .channelthe Sumfre-- quency; whichV is ,equal to.l the,4 input lfrequency; to.

the rst. l, frequency-conversion `stage, ofv- Said secondchannel'. w

15. A system for selectively producinganyone comprising a `crystal-contrclleel masterY osc'i1lator,

a` rst frequency selector vchannel for.producing` coarse frequency increments of! thel salme irequencystabilityv as -said- -osfci-llator,u Y a .sec0nd -fre qlienciY selectorv channel '-fqr producing `line fre--` quency increments ofthe same frequency -'stablitylof said oscillator,- a". frequency y multiplier channel, all of said char ne1s A being cent-rolled by said-ml ster cscillator, each of `s'.a.id. frequency'- Select@ Channels: heviri'e two, frleeueny ,Cerner-l sonlstagee which twost'ages: are 'excited loy` the same local` oscillator,:frequencyesofthat tha-:minute frequency to, therst :sta'geequals theloutputl153e, queneyl of.the,second stagecand isffreeefnomamf.. bient kchangesdn thetfrequencylcf -.the.1ocaL :oscilz-l.

l latonan .electron tube.- mxenconnectedito; said,N

three., channels and controlled-bythein respective output-s toproduce inthe output .ofufsaidemxer by; frequencyf. conversion the saidadesredizhigh. frequencylcarren nEEERENcneicnm The fol-lowing references are clrecordein the -le of -fthis --patentc UNITED- :STATE y'clr-VNT.Sl

Number Y Name Bate:A

1,854,986 Fitchk A1:r l 19:21932f 2,102,472l MayerV Dec.l 14; 1937 2,247,544; Daily July-ele 19411 2,340,364 Bedford: Feb'..1,=- 1944.1 2,369,268l1v Trevor.:. Feb.'` 1'3;` 194575 2,383,005 Marks Aug.y 21'; 1945"'- 2,406,932` Tunick1 Sep1',.13:1946vv 2,407,212y Tunickf': Septf.=`-3,1194l6f 

